1. Field of the Invention
This invention is directed to a method for managing color selection for windowing displays which display multiple computer program applications. More particularly, the inventive method manages color selection among a plurality of program applications, and/or a plurality of images in a single program application, displayed in a multiple windows environment on a single display screen.
2. Description of Prior Art
Window programs, or operating systems, which display multiple program applications on a single computer screen are well-known. Examples include the X-Windows program that runs in the UNIX environment, the Microsoft Windows program that runs in the DOS environment, and IBM's OS/2 operating system. Particularly, with regard to X-Windows, the operator may select a plurality of color tables for controlling the colors to be displayed when a given application program is active on the display screen. Active, as used herein, means the operator is currently working with that application. This would typically be indicated by the presence of the display cursor in the window of the active application. There are many more colors available to a display than are practical for storage in a color table. For example, if 8-bit bytes are used to express the intensity for each of the primary colors, red, green and blue, there are a total of 2.sup.24 possible colors that may be displayed. To store this many color choices is impractical; typically, the color table for a display screen contains 256 locations. For any given display, the system loads up to 256 of the possible 2.sup.24 color choices in the color table for the display. The window manager then uses colors from this active table to display all objects on the screen while the application associated with those color choices is active.
If during the switching from a first to a second application the active set of 256 colors is changed, the screen colors will change. This produces an annoying screen flashing effect to the user, as the user sees the display screen change colors when moving the cursor from one application window to the next application window. This screen flashing is sometimes referred to as the technicolor effect. This problem is most likely to occur when an application uses one or more video images. Such images contain multiple color choices that can soon use up the 256 choices available to the display.
The use of multiple color tables, or color maps, for different applications, or different images, in a single application is well known. It is also well-known to set pixel priorities by window so as to be able to overlay windows on the screen. Techniques for overlaying windows and displaying the correct color for each pixel are taught in U.S. Pat. Nos. 4,550,315; 5,091,720; and published European Patent Application 392,551. None of these patents or publication acknowledges the problem of the technicolor effect, or suggests any solution for the problem.